Inhibition of soluble epoxide hydrolase rescues cognitive deficits by preserving neurovascular integrity and attenuating glial and neuropathology in diabetic-related dementia

Diabetes mellitus (DM) is a major risk factor contributing to the development of Alzheimer's disease-related dementias (ADRD). While one of the early symptoms of both Alzheimer’s disease (AD) and DM-related ADRD is a reduction in cerebral blood flow, the underlying biological mechanisms driving this decline remain to be fully elucidated. Genome-wide association studies have linked AD/ADRD to single-nucleotide polymorphisms in the gene encoding soluble epoxide hydrolase (sEH), an enzyme we previously reported to be upregulated in the brains of an AD rat model. Our previous studies also demonstrated that chronic sEH inhibition with 1-trifluoromethoxyphenyl-3-(1-propionylpiperidin-4-yl) urea (TPPU) preserves hippocampal-dependent spatial learning and memory and improves cerebral hemodynamics in both AD and DM-ADRD models. In the present study, we found that chronic TPPU treatment (1 mg/kg/day) reduced sEH expression in the brain, improved cortical-based non-spatial recognition memory involving both cortical and hippocampal networks, and reduced anxiety in DM-ADRD rats. TPPU improved brain perfusion and normalized impaired whisker-evoked functional hyperemia, an effect associated with increased Kir2.1 expression and neurovascular coupling in cerebral capillaries. Furthermore, TPPU increased tight junction protein expression (ZO-1 and OCLN), mitigated capillary rarefaction, and suppressed astrocyte and microglial activation in DM-ADRD rats. At the cellular level, TPPU attenuated hippocampal neurodegeneration, restored the expression of synaptic proteins (PSD95 and SY38), and reduced levels of proinflammatory chemokines, including MCP-1, RANTES, and MIP-1α, in the hippocampus of DM-ADRD rats. In conclusion, TPPU preserves cognitive function in DM-ADRD by mitigating cerebrovascular dysfunction, neuroinflammation and gliosis, thereby preserving synaptic integrity and neuronal survival, and represents a promising therapeutic strategy for DM-ADRD.